1. Field of the Invention
The present invention relates to a forward check valve that controls a flow of a fluid in a forward direction, and to a fuel cell system including the forward check valve.
2. Description of the Related Art
A pressure reducing valve provided for passive driving and used in a small fuel cell is disclosed in Japanese Unexamined Patent Application Publication No. 2008-59093. The pressure reducing valve is configured so that, when the pressure of a fluid becomes a set pressure, the valve automatically opens and closes by making use of a pressure difference.
FIGS. 1A and 1B are each a sectional view of the pressure reducing valve that is disclosed in Japanese Unexamined Patent Application Publication No. 2008-59093. The pressure reducing valve includes a diaphragm 1, a piston 2, a valve housing 7, a valve seat 3, a valve body 4, a supporting portion 5, and a fixation portion 6. The diaphragm 1 is a movable section. The piston 2 is a transmission mechanism. The valve seat 3, the valve body 4, the supporting portion 5, and the fixation portion constitute a valve portion. The valve body 4 is supported along a periphery thereof by the supporting portion 5. The supporting portion 5 is defined by a resilient bar. The fixation portion 6 fixes the supporting portion 5 to the valve housing 7. Here, each of these members is a plate member. The pressure reducing valve is manufactured by joining each of these members together.
Pressure at a top portion of the diaphragm (movable section) 1 is P0, primary pressure at an upstream side of the valve is P1, pressure at a downstream side of the valve is P2, the area of the valve body 4 is S1, and the area of the diaphragm (movable section) 1 is S2. Here, from the equilibrium of the pressures, as shown in FIG. 1B, the condition for opening the valve is (P1−P2)S1<(P0−P2)S2. If P2 is higher than the pressure of this condition, the valve closes, whereas, if P2 is lower than the pressure of this condition, the valve opens. This makes it possible to maintain P2 at a constant value.
For example, a direct methanol fuel cell (DMFC) includes a pump that transports fuel (methanol). In general, although a valve-system pump is provided with a valve non-returning function, the valve-system pump is not provided with a valve forward check function (a function of checking a flow in a forward direction). If a pump that is not provided with a valve forward check function is used, when an upstream-side pressure (pressure in a forward direction) is applied to the fuel, the fuel flows even when the pump is not operating.
The temperature of a fuel cartridge that is built in a fuel cell system may become high due to the external environment, as a result of which high-pressure fluid may be discharged. This may cause excess fluid to be supplied to a fuel cell, and the pump to break in some cases. Accordingly, a valve that checks a flow in a forward direction if high-pressure fluid is applied (hereunder referred to as “forward check valve”) is demanded.
However, when manufacturing the pressure reducing valve disclosed in Japanese Unexamined Patent Application Publication No. 2008-59093 and shown in FIGS. 1A and 1B, it is necessary to fix the supporting portion 5 to the valve housing 7 by aligning the valve body 4 so that the valve body 4 comes into contact with or separates from a valve seat 3 in accordance with the displacement of the diaphragm 1. Therefore, it is necessary to precisely perform the alignment.
Since the pressure reducing valve disclosed in Japanese Unexamined Patent Application Publication No. 2008-59093 has a structure in which the supporting portion 5 is fixed to the valve housing 7 at the fixation portion 6, the height of the valve body is increased in correspondence with the thickness of the fixation portion 6.
Valve portions have individual differences due to, for example, manufacturing variations. Therefore, in the structure of the pressure reducing valve disclosed in Japanese Unexamined Patent Application Publication No. 2008-59093, pressurization of a valve seat by a valve portion differs greatly with each pressure reducing valve. That is, a pushing force required to open the valve when the piston 2 of the diaphragm 1 pushes down on the valve body 4 differs greatly with each pressure reducing valve. Therefore, in the structure of the pressure reducing valve disclosed in Japanese Unexamined Patent Application Publication No. 2008-59093, fluid control cannot be performed with sufficient reliability.